In MIG welding the arc is maintained between a metallic electrode (expendable, filler welding wire) and the work. The melting of the electrode supplies filler metal to the weld and is continuously fed into the weld metal pool. A shielding, inert gas fed through the welding head provides the necessary protective atmosphere for the weld. This known method of fusion welding is rapid and relatively inexpensive. However, difficulty has been encountered in machine guided welding operations where relatively light gauge metal plate seams are to be welded, the seams being irregular and intricately curved and the pieces to be welded not held to close dimensional tolerances. Under these conditions, the gap to be closed by the weld, applied by the rapidly traversing head, may be, at intervals, too wide, and defective welds result. One application where this difficulty has been encountered is in the welding of the curved, light gauge metal sheets forming the end plates or bridge members of burial casket cap components. Attempts have been made to overcome the problem by providing a reciprocating or back-and-forth motion to the welding head as it traverses the work. Such an arrangement is shown in Bartley U.S. Pat. No. 3,841,547. The back-and-forth motion of the welding gun, however, encounters difficulty where the seam to be welded is curved somewhat sharply because, in this situation, some means must be provided to maintain the back-and-forth motion path of the welding head transverse to the curved, non-rectilinear seam to be welded. The welding head must be properly oriented with relation to the curving seam to be welded as the head is rapidly machine guided over the work by the external guiding system. This requires providing relatively complicated and expensive mounting or coupling between the welding head and the external guidance system.
The apparatus of the present invention provides a relatively simple, uncomplicated means for moving the welding gun in a circular or orbital path as the welding head is machine guided over the work, the orbital path providing a relatively flat weld bead which fills the spaces between the parts being welded even though the seam is intricately or sharply curved.